add block may cause memory leak in safari

[sheeeeep]

Describe the bug

After add some blocks and delete them, I found the memory usage is extremely high.

To Reproduce

Steps to reproduce the behavior:

1. Visit blockly demo in safari (my safari version is 10.15.4)
2. open safari's devtool , choose timeline, and start record.
3. add some blocks and then delete them casually.

Expected behavior

Before step3, the memory usage is 70M+.
After step3, the memory usage is 200M+, even though the workspace is still empty.

Screenshots

Desktop:

• OS: mac os
• Browser: safari
• Version: 10.15.4

Additional context

The memory usage increased in PAGE.

If we use it in mobile device that memory capacity is pretty small, It may cause some performance problem.

[sheeeeep]

This problem maybe born from following code:

When use audio.cloneNode() to play sound, Safari seems like not release cloned node's memory usage. I made a simple demo to test it.

var playButtonElement = document.getElementById('playButton');
var audio = new Audio();

audio.src = './click.mp3';
audio.volume = 1;

playButtonElement.addEventListener('click', () => {
    var mySound = audio.cloneNode();
    mySound.play();
    mySound.onended = function() {
        mySound.remove();
        mySound = null;
    }
})

I try to inform Safari do garbage collect but it didn't works, maybe it is Safari's bug ？

And I would like to know why use cloned audio node to play instead of play audio node directly?